Method Of Insulating Electric Conductors



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u. TESLA.

METHOD OF INSULATING ELECTRIC CDNUUCTDRS.

' (Applicltion filed Sept. 21, 1900.)

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UNITED STATES.

PATENT OFFICE.

NIKOLA,'IESLA, OF NEW YORK, N. Y.

METHOD OF INSULATING ELECTRIC CONDUCT ORS.

SPECIFICATION forming part of Reissued Letters Patent No. 11,865 datedOctober 23, 1900.

Original No. 665,838, dated August 14, 1900. Application for reissuefiled September 21, 1900- Berill No. 30 722.

To all whom it may concern.-

Beit known that I, NIKOLA TESLA, acitizen of the United States, residingin the borough of Manhattan, in the city, connty, and State of New York,have'invented certain new and useful Improvements in Methods ofInsulating Electric Conductors, of which the following is aspecification, reference being bad to the accompanying drawings.

It has long been known that'*;many sub stances which are more or lessconducting when in the fluid condition becomejnsulators when solidified.Thus water, which is in a'measure conducting, acquires insulatingproperties when converted into ice. The existing information on thissubject, however, has been heretofore of a. general nature only andchiefly derived from the original observa t-ions of Faraday, wh'oestimated that the substances upon which he experimented, such as waterand aqueous solutions, insulate an electrically-charged conductor aboutone hundred times better when rendered solid by freezing, and no attempthas been made to improve the quality of the insulation obtained by thismeans or to practically utilize it for such purposes as are contemplatedin my present invention. In theconrse of my own investigations,moreespeciall y those of the electric properties of ice, I havediscovered some novel and important facts, of which the more prominentare the following: first, that under certain conditions, when theleakage of the electric charge ordinarily taking place 'is. rigorouslyprevented, ice proves itself to be a much better insulator than hasheretofore appeared; second, that its insulating properties may be stillfurther improvedby the addition cf other bodies to the water; third,thatthe dielectric strength of ice or other frozen.

aqueous substance increases with the reduct-ion'of temperature andcorresponding increase of hardness, and, fourth, that these bodiesafford a still more effective insulation for conductorscarryingintermittent or alternating currents, particularly of'highrates,

surprisingly-thin layers of ice being capable of withstandingelectromoti've forces of many hu ndrcds and even thousands of volts.These and other observations have led me to their:- vention of a novelmethod of insulating con- 7 above facts and advantageous in theutilization of electrical energy for industrial and commercial purposes.

This method consists in insulating an electric conductor by freezingOrsolidifyiugand maintaining in such state the material surrounding orcontiguous to the conductor, using for the purpose a gaseous coolingagent circulating through one or more suitable channels extendingthrough or in proximity to the said material.

Iii the practical carrying out of my method I may employ a hollowconductor and pass the cooling agent through the same, thus freezing thewater or other medium in contact with or close to such conductor, or mayuse expressly for the circulation of the cooling agent an independentchan'neland freeze or solidify the adjacent substance in which anynumber of conductors may be embedded. The conductors may be'bare orcovered with some material which is capable of keeping them insulatedwhen it is frozen or solidified.

The frozen mass may be in direct touch with the surrounding medium, orit may be'in a degree protected from contact with the same by I aninclosure more or less impervious to heat. The cooling agent may be anykind of gas, as atmospheric air,'oxygen, carbonic acid, ammonia,illuminating-gas, or hydrogen. It may be forced through the channel bypressure or suction produced mechanically or otherwise.

It may be continually renewed or indefinitely used, being driven backand forthor steadily section, or partlysmconstructive details to bedescribed.

InjFi'g. I, C is a hollow conductor, such'as a steel tube, laid infu.body of water and communicating with a'reser'voir 1'', butelect ricallyinsulated from the same atj. A pump or compressor p, of any suitableconstruction, connects r with another similar tank r, productors,rendered practicable by reason oftlie l vided with an inlet-valve '0'The air or other 2 11,ses

gas which is used as the cooling'agententering through the valve-1: isdrawn through the tank 'r'and pu m p 1) into the reservoirr', escapingthence through the-conductor C- under any desired pressure which may beregulated by a valve 1;. Both the reservoirs r and r" are kept at a lowtemperature by suitable means, as by coils or tubes t t and t 5, throughwhich any kind of refrigerating fluid may be circulated, some provisionbeing preferably madefor adj listing the flow of the same, as byvalves-v. I The gas continuously passing through the tube or conductor 0beingvery cold will freeze and maintain in this state the water incontact with or adjacent to the conductor and so insulate it. Flangedbushin gs i 1?. of non-cond noting materialnnay be used'to prevent theleakage ofthe current which would otherwise occur, owing to theformation of a superficial film of moisture overthe ice projectingout ofthe water. The tube being kept insulated bythis means may then beemployed in'zthemanner of an ordinary telegraphic orherjcable byconnecting either or bothvof ftb ie-terminals b b in a eir'cuitjincluding theearth.

. Inf na'ny cases icw beef advantage to cover the hollowcondnctofr witha thick layer of some cheap material, as felt, this beinginqdicated by(J in Fig.2. Such-. a covering,

penetrable' by water, would be ordinarily. of littleorno use; butwhenembedded in the ice i't-iinprovesthe insulating qualities of the'jsame. In this instance it furthermore serves 5 tog'restly reduce thequantity of ice required, rate-of melting, and thefinllux of heatwaffrom the outside,'t-h'us diminishing the ex- -;f-penditurefo'f energynecessary for the maintenauce of normal working conditions. As -,oregards this energy and other; particulars of I [importance they willvaryaccording to the special demands in each case.

Generally considered,the'cooling agent will have to carry away heat at arate suflicient to keep the conductor at the desired tetn perature andto maintain a layerfof the required thickness of thesubstancesurrounding it in a frozen state, compensatingcontinually fortheheat flowing in through the layer and wall so of the conductor andthat generated by mechanical and electrical friction. To meet theseconditions, its cooling capacity, which s dependent on the temperature,density,

-.velocity,and specific heat,will be calculated 5'5 the help of data andformulae familiar to engineers.

fo' r- .'the use contemplated; but in exceptional nstances some othergas, as hydrogen, may be resorted to, which will permit a much 6ogreaterrate of cooling and a lower temperatnre to be reached. Obviouslywhichever be employed it should before entering the hollow conductor orchannel be thoroughly dried and separated from-all which bycon- 'densation and deposition-or otherwise might 1 cause an obstruction to itspassage. For these purposes apparatus may employed tricity for indnstrial Air will be, as a'rule, suitable: "plan.

which is well known and which it is unnec essary to show in detail. I

Instead of being wasted at the distant sta- 10 tion the cooling agentmaybe turned to some profitable use. Evidently in the industrial andcommercial exploitation of my invention any kind of cooling agentcapable of meeting the requirements maybe conveyed from one to anotherstation ,and there utilized for refrigeration, power, boating, lighting,sanitation, chemical processes, or any other purpose to which itmaylenditself, and thus the revenue of the plant may be increased.

H As to the temperatnreof the conductor, it will be determined by thenature of its use and considerations of economy. Forinstance, if it beemployed for the transmission of telegraphic messages, when the loss inelectrical friction may be of no consequence, a very low temperature maynot be required; but if it be used for transmitting large amounts ofelectrical energy, when the frictional waste may be a serious drawback,it will be desiro able to keep it extremely cold. The attainmentof thisobject will be facilitated by any provision for reducing as much aspossible the flowing in of the heat from the surround ing medium.Clearly the lower the temperatnre of the conductor the smaller will bethe loss in electrical friction; but, on the other hand, the colder "theconductor the greater will be the influx of heat from the outside andthe cost of cooling agent.

From such I00 and similar considerations the temperature secnring'thehighest economy will be ascertained.

Most frequently in the distribution of elecnrposes, as in my sys- :05tom of power transmission by alternate currents, more than one conductorwill be required, and in such cases it may be convenient to circulatethe cooling agentin a closed path formed by the conductors A plan of Ito this kindis illustrated in Fig. 3, in which 0' and 0 represent twohollow conductors embedded in a frozen mass underground andcommunicating, respectively; with thereservoirs R and R", which'areconnected bya re- 1'15 ciprocating or other suitable pu'm'p P. Coolingcoils or tubes T' T and 'l T, with regulating-valves 'v"v" are employed,which are' similar to and 'serve the same purpose as those shown inFig. 1. Other features of m similarity, though unnecessary, are.il|ns.-4:. trat-ed to facilitate an understanding of the A three-way valve V,is provided, which when placed with its lever 1 as indicated allows thecooling agent to enter 1:; through the tubes u u"' and pump P, thusfilling the reservoirs R R. and hollow con, ductors .C C; but whenturned ninety degrees the valve-shuts off the communication .to theoutside through the tube to and estab- 13c lishee a connection betweenthe reservoir R.

and pump P through the tubes 11. and u, thus permitting the coolingagent to be circulated in the closed path 0' C R u-n' I R by the nectingthe conductors to the circuit at each station.

In laying the conductors, as 0' 0 whatever be their number,.a-trenchwill generally be dug and a trough, round or square, as T, 0! smallerdimensionsthan the trench, placed in the same, the intervening spacebeing packed with some material (designated by M M M) more or lessimpervious to heat,

as sawdust, ashes, or the like, Next the con-' doctors will be put inposition and temporarily supported in any convenient manner,

and, finally, the trough will be filled with first-er or other substanceW, which will be gradually frozen by circulating the cooling agent inthe closed path, as before described. .Usually the trench will notbe-level, but will follow the undulations of the ground, and this willmake it necessary to subdivide the trough in sections or to effect thefreezing of the substance filling it successivelyin parts. This beingdone and "the conductors thus insulated and-fixed, a layer of the sameor similar material M M M will .be placedon the top and the wholecovered with earth or.

pavement. The trough may be of metal, as

sheet-iron, and in caseswhere the ground is used as the return-circuitit may serve as a main, or it may be of any kind of material more orless insulating. :Figs; 4 and 5 illustrate in crosssection two suchunder-- ground troughs '1" and T", of sheet metal,

with their adiathermanousinclosures, (designated M and M",respectively,) each trough containing a single central hollow conductor,as O O. In the first case the insulation W is supposed to'be iceobtained by freezing water preferably freed of air in order to excludethe formation ot'dangerous bubbles or cavities while in the second casethe frozen mass W is some aqueous or other substance or mixture highlyinsulating when in this condition.

It should be stated that in many instances it may be practicable todispense with a trough by resorting to simple expedients in the placingand insulating of the conductors. In fact, for some purposes it may besufiicien t to simply cover the latte} with a moist mass, as cement orother'plastic material, which so long as it is kept at a very lowtemperature and frozen hard will' afford adequate insula tion.

Another typical way of carrying out my invention, to which reference hasalready been made, is shown in Fig. 6, which represents thecross-section of a trough, the same in other respects as those beforeshown, but containing instead of a hollow conductor any kind of pipe orconduit. L. The cooling agent may be driven in any convenient mannerthrough the pipe for the purpose of freezing the wateror other substancefilling the trough, thus insulating and fixing a number of conductors cc0. Such a plan may be particularly suitable in cities for insulating andfixing telegraph and telephone wires or the like. In such cases anexceedingly-low temperatu-re of the cooling agent may not be-required,and the insulation will-be obtained at, the expense of little power. Theconduit L may, however, be used simultaneously for conveying anddistributing any kind of gaseous cooling agent for which th'er'isademand through the district. Obviously'two'such con similar du its maybe provided and used in a mannerv as the conductors C 0. g

It will often-be desirable to place in the saine trough a great numberof wires or conduct-ore serving for a variety of purposes. In such acasea plan may be adopted which is .-illustrated in Fig. 7, showing a troughsimilar-- to that in Fig. 6 'with the conductors in cross-section. Thecooling agent maybe in this instance circulated, as in Fig. 3 orotherwis'e, through the two hollow conductors (3 and C, which iffound-advantageous may be covered with a layer of cheap material 01pm,such as will improve theirinsulation, but not. preventthe freezing orsolidification of the surroundingsubstance W. The tubular-conductors C0, preferably of iron, may then serve to con vey heavy currents forsupplying light and power,while the smallones c c' o embedded in the iceor frozen mass, may be usedtor any oth'erpurposes.

.While my invention contemplates, chiefly, the insulation of conductorsemployed in the transmission of electrical. energy to a distance, it mayhe, obviously, otherwise usefully applied. In some'instances, forexample, it may be desirable to insulate and sup port va conductor inplaces as is ordinarily done by means of glass or porcelain insulators.This may be eflfected in many ways by conveying a cooling agent eitherthrough the conductor-or through an independent channel and'freez'ing orsolidifying any kind of substance, thus enabling it to serve thepurpose. Such an artificial insulating-support.- is illustrated in Fig.8, in which a represents avessel filled with water or other substanceto, frozen by the agent circulating through the hollow contiuctor C",which is thus insu- To improve the insulated and supported. lation onthe top, where it is most liable to give way, a layer of some substancew, as oil, may be used, and the conductor may be covered near thesupport with insulation 11 i, as shown, the same extending into the oil,for reasons well understood.

Another typical application of my invenondary conductors, bare orinsulated, of a transformer, which are wound on a core N and immersed inwater or other substance W,

contained in a jar; II, and, as before stated,

convenient manner, as through the hollow primary I", for the purpose offreezing the substance W. Flanged bushings'rl d and oilcupsee, extendinginto the frozen mass, illustrate suitable means for insulating the endsofthe two conductors and preventing the leakage of the currents, Atransformer as described is especially fitted for use with currents ofhigh frequency when a low temperature of the conductors is particularlydesirable, and ice affords an exceptionally-effect.- ive insulation.

It will be understood that my in vcntion may be applied in manyotherways, that the speclal means here described will be greatly variedaccording to the necessities, and that in each case many expedients willbe adopted which are well known to engineers and electricians and on"which it is unnecessary to dwell. However, it may be useful to statethat in some instances a special provision will haveto be made foreffect-ing a uniform cooling of the substance surrounding theconductor-throughout its length. Assuming in Fig. 1 the cooling agent toescape at the distant end freely into the atmosphere or into areservoirmaintained at low pressure, it wil in passing through thehollow conductor 0 move with a velocity steadilyincreasing toward theend, expanding isothermally,or nearly so, and

,hence it will cause an approximately-uniform formation of ice along theconductor. In the plan illustrated in Fig. 3 a similar result will be ina measure attained, owing to the compensating effect of the hollowconductor C and O, which may be still further enhanced by reversingperiodically the direction of the flow in any convenient manner; but inmany cases special arrangements will have to be employed to render thecooling more or less uniform. 5, and 6, instead of a single channel twoconcentric channels L and L may be provided and the cooling agen tpassed through one and returned through the other, as indicated,diagrammatically, in Fig. 10. In this and any similar arrangement whenthe flow takes place in opposite directions the object aimed atwill bemore completely attained by reducing the temperature of the circulatingcooling agent at the distant station, which may be done by simplyexpanding it into a large reservoir, as R", or cooling it by means of atube or coil '1 or otherwise. Evidently in'the case illustrated theconcentric tubes may be used as independent conductors if insulated fromeach other and from the ground by the frozen or solidified substance.

Generally in the transmission of electrical For instance, referring toFigs. 4,

conveyed. 'In such cases a fairly-uniform freezing of the insulatingsubstance will be attained without difficulty by the c0mpensatingcfIe-et of the oppositely-circulating cooling agents. In large plants ofthis kind when the saving of electrical energy in the transmission isthe most important considerv ation or when the chief object is to reducethe cost of the mains by the employment of cheap metal, as iron orotherwise, every effort will be made to maintain the conductors at thelowestpossible temperature, and well- 'known refrigerating processes, asthose based on the regenerative principle, may be resorted to, and inthis and any other case thehollow conductors orchannelsinstead of merelyserving the purpose of conveying the cooling agent.

may themselves form active parts of the refrigerating apparatus.

From the above description it will be readily seen that my inventionforms a fundamental departure in the principle from'the establishedmethods of insulating conductors employed'in the industrial andcommercial application of electricity. It aims, broadly, at

obtaining insulation by the continuous ex-,

penditure of a moderate amount of energy instead of securing it only byvirtue of an in- .herent physical property of the material used Moreespecially, its object is as heretofore. to provide, whenand whereverrequired, insulation of high ,quality, of any desired thickness, andexceptionally cheap,'and to enable the transmission of electrical energyunder conditions of economy heretofore unattain-' able and at distancesuntil now impracticable by dispensing with the necessity of using costlyconductors and insulators.

What I'claim as my invention is- 1. The method of insulating electricconductorsherein described which consists in impartinginsulatingproperties to material surrounding or contiguous to the saidconductor by the continued action thereon of a gaseouscooling agent, asset-forth.

Q2. The method of insulating electric condoctors herein described whichconsists in reducing to and maintaining in a frozen or 'solidlfiedcondition the material surrounding or contiguous to the said conductorby the action thereon of a gaseous coolingagent maintained incirculation through o'ne or more channels as set forth,

3. The method of insulating electric conductors herein described whichconsists in surrounding or supporting the conductor by r when in afrozen or solidified state, and main- 11,ses 5 mining 'the material insuch a state by the circulation through one or more channels extendingthrough it of a gaseous cooling agent, as set forth.

4. The method of insulating an electric cond uctor which consists insurrounding or supporting -said conductor by a materialwhich acquiresinsulating properties when frozen or solidified, and maintaining thematerial in such state by passing a gaseous cooling agent continuouslythrough a channel in said conductor, as set forth.

5. The method of insulating electric conductors, which consists insurronnding'or su pporting the said conductors by a material which acquires insulating properties when in a frozen or solidified state, andmaintaining the material in such state by the continued applicationthereto of a gaseous cooling agent, asset forth.

6. The'method of insulating conductors herein set forth which consistsin surrounding or supporting the conductors by a material which acquiresinsulating properties when in a frozen orsolidified state, andmaintaining the material in such state by the circulation of a gaseouscooling agent through a circuit of pipes or tubes extending through thesaid material as set forth.

7. The method of insulating electric conductors which consists in layingor supportr ing the conductors inst-rough or conduit filling the troughwith a nialerial which acquires insulating properties when frozen orsolidi-- as to freeze or solidify the material, as set forth.

a 8. The method -of insulating electric cond uctors which consists inembedding the same in a moist or plastic compound which acquiresinsulating properties when in a frozen or solidified state, andmaintaining the compound in such state by circulatinga gaseous coolingagent through one or more channels extending through the compoundfas setforth.

9. The method of insulating electric conductors which consists in layingor support mg the conductors in a trough or conduit, filling the troughwith a material which acquires insulating properties when frozen orsolidifled, protecting the trough from the surround-. ing medium inwhich it is laid by an adiathermanonsinclosure, and then freezing orsolidifying the-material surrounding the con.-

ductors and maintaining the same in such. state by circulating a gaseouscooling agent.

through one or more channels. extending through the same, as set forth.

v NIKOLA TESLA. Witnesses:

DRURY W, COOPER, J 01m 0. KERR.

